Lubricants in commercial use today are prepared from a variety of natural and synthetic base stocks admixed with various additive packages and solvents depending upon their intended application. The base stocks typically include mineral oils, poly alpha olefins (PAO), gas-to-liquid base oils (GTL), silicone oils, phosphate esters, diesters, polyol esters, and the like.
Oxidation resistance of a lubricant is the key to achieve long oil life by controlling oil viscosity and total acid number (TAN) increase, minimizing deposit (varnish/sludge) formation and maintaining good heat transfer and lubricating properties. For industrial lubricants, the oxidation performance relies mainly on the basestocks used.
Alkylated naphthalene (AN) is a base stock used in conventional automotive and industrial lubricant products. A double ring molecule such as naphthalene has better oxidation performance than single ring aromatic. The superior oxidation performance of AN is limited to its lower molecular weight product. As the molecular weight AN increases through addition of alkyl chain to the aromatic ring, its oxidation performance begins to suffer. At the same time, there is a need for higher molecular weight/viscosity AN in order to reduce interaction with the elastomer seal component. Conventional AN products cannot meet both of these objectives namely, an increase in viscosity while retaining oxidation performance and provide adequate seal manageability.
Alkyl aromatic basestocks have been used to improve the oxidation and hydrolytic stabilities of lubricant formulations. One drawback of the lower molecular weight alkyl aromatic basestock is its seal management ability from its interaction with the elastomer components in the equipment resulting in swelling and degradation of the seal materials that can lead to leakage of the lubricant.
One way to reduce the interaction of basestock and elastomers is to increase the molecular weight or size of the basestock molecule. Conventional way to increase the molecular weight of alkyl aromatic basestocks is by introducing alkyl chains to the aromatic ring. This approach however increases the paraffinic nature and reduces the aromatic content of the molecule. As the basestock became more paraffinic, its oxidation stability decreases as well.
Alkyl aromatics, specifically, low viscosity alkyl naphthalene, has been shown to provide improvement in oxidation performance in a lubricant formulation. However, its impact on elastomer compatibility has limited its use to lower concentration.
Therefore, there is a need for a base stock that can meet both of the above objectives: increase viscosity while retain oxidation performance and elastomer compatibility.
The present disclosure also provides many additional advantages, which shall become apparent as described below.